The molecular record of metabolic activity in the subsurface of the Río Tinto Mars analog

In the subsurface, the interplay between microbial communities and the surrounding mineral substrate, potentially used as an energy source, results in different mineralized structures. The molecular composition of such structures can record and preserve information about the metabolic pathways that have produced them. To characterize the molecular composition of the subsurface biosphere, we have analyzed some core samples by time-of-flight secondary ion mass spectrometry (ToF-SIMS) that were collected in the borehole BH8 during the operations of the Mars Analog and Technology Experiment (MARTE) project. The molecular analysis at a micron-scale mapped the occurrence of several inorganic complexes bearing PO3-, SOx(2to4)-, NOx(2,3)-, FeOx(1,2)- SiO2-, and Cl-. Their distribution correlates with organic molecules that were tentatively assigned to saturated and monounsaturated fatty acids, polyunsaturated fatty acids, saccharides, phospholipids, sphingolipids, and potential peptide fragments. SOx- appear to be mineralizing some microstructures larger than 25 microns, which have branched morphologies, and that source SO3-bearing adducts. PO3-rich compounds occur in two different groups of microstructures which size, morphology, and composition are different. While a group of >40-micron sized circular micronodules lacks organic compounds, an ovoidal microstructure is associated with m/z of other lipids. The NO2-/NO3- and Cl- ions occur as small microstructure clusters (<20 microns), but their distribution is dissimilar to the mineralized microstructures bearing PO3-, and SO3-. However, they have a higher density in areas with more significant enrichment in iron oxides that are traced by different Fe-bearing anions like FeO2-. The distribution of the organic and inorganic negative ions, which we suggest, resulted from the preservation of at least three microbial consortia (PO4-, and NO2-/NO3-mineralizers PO4-lipid bearing microstructures), would have resulted from different metabolic and preservation pathway

Protection of Possessors in Classical Roman Law -From the Viewpoint of Buyer Protection- (2)

We studied the formation of Mg-rich carbonate in culture experiments using different aerobic bacterial strains and aqueous Mg/Ca ratios (2 to 11.5) at Earth surface conditions. These bacteria promoted the formation of microenvironments that facilitate the precipitation of mineral phases (dolomite, huntite, high Mg-calcite and hydromagnesite) that were undersaturated in the bulk solution or kinetically inhibited. Dolomite, huntite, high Mg-calcite, hydromagnesite and struvite precipitated in different proportions and at different times, depending on the composition of the medium. The Mg content of dolomite and calcite decreased with an increasing Ca concentration in the medium. The stable carbon isotope composition of the Mg-rich carbonate precipitates reflected the isotope composition of the organic compounds present in the media, suggesting that microbial metabolism strongly influenced the carbon isotope composition of biomediated carbonates. We observed that Ca-enriched carbonate precipitates have relatively low carbon isotope composition. These results provide insights into the mechanism(s) of carbonate formation in natural systems, and they are of fundamental importance for understanding modern environments in which carbonate minerals form as a window into the geologic past

Geobiology of a lower Cambrian carbonate platform, Pedroche Formation, Ossa Morena Zone, Spain

The Cambrian Pedroche Formation comprises a mixed siliciclastic-carbonate succession recording subtidal deposition on a marine platform. Carbonate carbon isotope chemostratigraphy confirms previous biostratigraphic assignment of the Pedroche Formation to the Atdabanian regional stage of Siberia, correlative to Cambrian Series 2. At the outcrop scale, thrombolitic facies comprise ~. 60% of carbonate-normalized stratigraphy and coated-grains another ~. 10%. Petrographic point counts reveal that skeletons contribute at most 20% to thrombolitic inter-reef and reef-flank lithologies; on average, archaeocyath clasts make up 68% of skeletal materials. In contrast, petrographic point counts show that skeletons comprise a negligible volume of biohermal and biostromal thrombolite, associated nodular carbonate facies, and ooid, oncoid and peloid grainstone facies. As such, archaeocyathan reefal bioconstructions represent a specific and limited locus of skeletal carbonate production and deposition. Consistent with data from coeval, globally dispersed lower Cambrian successions, our analysis of the Pedroche Formation supports the view that lower Cambrian carbonates have more in common with earlier, Neoproterozoic deposits than with younger carbonates dominated by skeletal production and accumulation. © 2013 Elsevier B.V.Jessica R. Creveling, David Fernández-Remolar, Marta Rodríguez-Martínez, Silvia Menéndez, Kristin D. Bergmann, Benjamin C. Gill, John Abelson, Ricardo Amils, Bethany L. Ehlmann, Diego C. García-Bellido, John P. Grotzinger, Christian Hallmann, Kathryn M. Stack, Andrew H. Knol

The environment of early Mars and the missing carbonates

A model is presented in which the aqueous conditions needed to generate phyllosilicate minerals in the absence of carbonates found in the ancient Noachian crust are maintained by an early CO2-rich atmosphere, that, together with iron (II) oxidation, would prevent carbonate formation at the surface. After cessation of the internal magnetic dynamo, a CO2-rich primordial atmosphere was stripped by interactions with the solar wind and surface conditions evolved from humid to arid, with ground waters partially dissolving subsurface carbonate and sulfide minerals to produce acid-sulfate evaporitic deposits in areas with upwelling ground water. In a subsequent geochemical state (Late Noachian to Hesperian), surface and subsurface acidic solutions were neutralized in the subsurface through interaction with basaltic crust, allowing the precipitation of secondary carbonates. This model suggests that, in the early Noachian, the surface waters of Mars maintained acidity because of a drop in temperature. This would have favored increased dissolution of CO2 and a reduction in atmospheric pressure. In this scenario, physicochemical conditions precluded the formation of surface carbonates, but induced the precipitation of carbonates in the subsurface